This invention relates to a device for processing semiconductor wafers or glass photomask plates, and in particular, to an improved rinser/dryer which minimizes the vibration during rotation of the carrier containing the wafers or photomask plates, and which further minimizes particulate contamination level.
The production of integrated circuits requires the use of semiconductor wafers or substrates. The processing of the semiconductor wafers requires multiple steps through which various layers of material are deposited and processed on the wafer substrate. The substrates themselves are typically of circular shape, several inches in diameter, with many wafer disks now being 100-150 mm in diameter. The wafers are very fragile, typically being made of glass or ceramic and having a thickness in the neighborhood of 0.025 inches.
The processing of the materials deposited upon these fragile substrates requires that the wafers be rinsed or coated with numerous solutions at various stages of the processing. At some stage almost all wafers require a rinsing and drying. It is more efficient if the washing and drying can be completed by a single machine. A uniform rinsing of the wafers can best be achieved by rotating the wafers while spraying them from a stationary nozzle. Since a number of wafers are placed in a carrier for ease of handling, it is more efficient to handle all the wafers simultaneously, in the carrier, during the rinsing/drying stage.
Various processing devices have been developed to complete this rinse/dry cycle. One such device is described in U.S. Pat. No. 4,300,581, to Thompson, in which a wafer carrier is placed into a frame that is rotated while stationary nozzles inject a fluid to rinse the wafers, or alternately inject heated gas to dry the wafers.
The Thompson patent has the frame containing the carrier enclosed, and sealed from the inside of a tub in order to inhibit contamination of the wafers during processing. The drive which rotates the frame is also sealed from the inside of the tub, by a rotational seal. This seal is a load bearing seal, subject to wear and degradation which in turn generates particulate contaminants. Thus, there is a need for a seal between the drive and the rotated frame which does not generate contaminants. It is an object of this invention to provide such a seal.
Too minimize the particulate contaminants which enter the tub and contaminate the wafers, at least one device uses a magnetic fluid in the seal. The magnetic fluid seal is subject to evaporation of the carrier fluid which degrades the effectiveness of the seal. Additionally, the location of the seal inhibits checking the fluid level and replacing lost fluid. Thus, there is a need for a seal which requires little inspection and is easy to maintain. It is an object of this invention to provide such a seal.
The rotating frame in the Thompson device is driven by a motor through a belt and pulley arrangement. This belt and pulley arrangement not only consumes a large amount of space, but introduces flexibility between the motor and the rotating frame which can exacerbate the oscillations occurring in the cantilever, but rotating frame. Since vibration of the carrier and wafers can damage the fragile wafers, it is desirable to reduce or minimize the amount of vibration introduced into the wafer carrier. It is an object of this invention to reduce the vibrational force exerted on the wafers during rinsing/drying. It is also important that vibration of the tub and any enclosing structure be minimized. Thus, it is a further object of this invention to minimize the vibration transmitted to the enclosing structure and housing.
The Thompson device also contained a vent in the door through which the carrier and wafers were loaded into the apparatus. This vent allows ambient air to carry contaminants into the tub and contribute to the contamination of the wafers in the apparatus. This contamination was exacerbated during the rinsing cycles when air was sucked through the vents by vacuum created by the withdrawing of rinse water. This suction could entrain far heavier particles in the incoming air stream than might normally pass through the vent in the Thompson apparatus. Thus, a device is needed which eliminates the contamination by ambient air during the rinsing cycle. It is an object of this invention to provide this reduction in contamination.